This invention relates to apparatus and manufacturing methods for pressure sensors that employ pressure-sensitive diaphragms. It relates in particular to apparatus and assembly methods, including mechanical and electrical features, for a modular sensor sub-assembly having a pressure-sensing element mounted on a substrate, and having electrical interconnections between the sensing element and accessible terminals.
As used herein, a pressure-sensing element is a component of a pressure sensor and is structured as a solid-state pressure-sensing device that mounts a thin silicon diaphragm above an open chamber. Pressure variations cause the diaphragm to deflect into and out of the chamber. The deflections cause changes in an electrical parameter, typically capacitance or resistance, and in turn generate a signal indicative of pressure.
In one prior pressure-sensing element, the signal is transmitted to electrical terminals located proximal to the pressure-sensing element and extending through and away from the sensor substrate for connection to external electronics.
This configuration, however, is relatively difficult and costly to manufacture and is prone to performance degradation. For example, in one known prior practice, the electrical terminals are molded through the substrate and can trap air or leak air in a manner that detracts from the desired pressure-sensing performance. The sensor wire bands are also prone to damage from improper cleaning and other misuse.
Further, the use of a pressure-sensing element in hostile environments typically requires that the pressure sensor be coupled, by way of a pressure-responsive fluid, to an isolation (ISO) diaphragm mounted on a supportive housing or "header". This configuration forms an ISO sensor in which the pressure-sensing element is protected from contact with the hostile environment. One of the many applications of an ISO sensor is in an infusion pump, where the hostile environment includes cleaning solutions, blood, urine and other fluids.
A conventional ISO infusion pump sensor has a flexible silicone ISO diaphragm and a medical grade plastic header. The ISO diaphragm communicates the pressure forces in the blood substitute to the pressure-sensing element by a non-corrosive, inert fill fluid or pressure-responsive gel.
However, the pressure-sensing element in this prior ISO sensor is still subjected to relatively hostile forces that can act on the pressure-responsive gel between the element and the ISO diaphragm. One source of the relatively hostile forces that can act on the gel arises from improper handling or cleaning of the sensor. During these conditions, one portion on the isolation diaphragm can be pressed sufficiently so that other portions of the diaphragm bulge. This flexure of the diaphragm can cause movement of the gel around the wire bands sufficiently to fatigue or brush them. Extreme localized pressure on the isolation diaphragm can, in addition, damage the diaphragm of the sensing element.
It is accordingly an object of this invention to provide an improved pressure sensor and associated manufacture methodology that are free of the afore-mentioned difficulties.
It is another object of this invention to provide an improved apparatus and manufacturing method that attain a modular pressure sensor that is less difficult and costly to manufacture than comparable prior sensors formed with leads therethrough.
It is a further object of the invention to provide an improved ISO sensor for use in an infusion pump and like hostile environments.
More particular, an object of the invention is to provide a modular pressure sensor apparatus, and an associated manufacturing method, which are less prone to performance degradation inherent in like pressure sensors currently available.
Other objects of the invention will be apparent from the following description.